header {
    background-color: darkred;
    height: 100px;
}

article {
    background-color: mediumvioletred;
    height: 300px;
    margin: 0 100px;
}

.middle {
    background-color: yellow;
    float: left;
    width: 100%;
    height: 250px;
}

.left {
    background-color: red;
    width: 100px;
    left: -100px;
    height: 300px;
    float: left;
    margin-left: -100%;
    position: relative;
}

.right {
    background-color: blue;
    width: 100px;
    right: -100px;
    height: 300px;
    margin-left: -100px;
    position: relative;
    float: left;
}

footer {
    background-color: green;
    height: 100px;
}